Speed control for an internal combustion engine of a motor vehicle

ABSTRACT

A control system for controlling the speed of an internal combustion engine of a motor vehicle wherein the control system provides open loop control of the fueling rate of the engine whereby the engine fuelling rate is controlled as a function of the engine speed when the engine is free of any operator demand thereon and when the motor vehicle is moving above a predetermined vehicle speed.

This invention relates generally to the control of an internalcombustion engine of a motor vehicle including motorcars, trucks,motorcycles, scooters, snowmobiles and all-terrain-vehicles, and inparticular to the control of the idle speed of the engine. The inventionis applicable for motor vehicles having either a manual or an automatictransmission, and for both two stroke or four stroke internal combustionengines.

The term "idle speed" refers to the engine speed when there is nooperator initiated demand on the engine which may relate to, forexample, when the vehicle is stationary or when the vehicle isfreewheeling down a hill.

BACKGROUND OF THE INVENTION

It is known to use electronic engine management systems for controllingthe operation of an engine within a motor vehicle. It is also known tohave a control system for performing "closed loop idle control" tocontrol the idle speed of the engine. This is a control strategywhereby, typically, the actual idle speed of the engine is compared to adesired target value idle speed at regular intervals. The engine idlespeed is returned or adjusted to that target value when any deviationfrom that target value occurs.

In conventional homogeneous charge internal combustion engines, theengine speed and the idle speed in particular are typically controlledby a throttle valve controlling air flow to the engine. In such anengine, the control system will normally define idle as being when thethrottle is closed. In contrast, in the case of engines such as theApplicant's stratified charge, air assisted, fuel injected engine, theengine speed is increased or decreased at idle by respectivelyincreasing or decreasing the fuelling rate when under closed loop idlecontrol. Accordingly, in such an engine, the control system maypreferably define idle as being when the accelerator pedal of thevehicle is fully disengaged. Typically, the fuelling rate is controlledby varying the opening time, commonly known as the "pulse" time, of thefuel injectors and therefore changing the amount of fuel injected intothe cylinders of the engine. The fuel based control system of theApplicant's engine therefore uses the fuelling rate as the primarycontrol parameter and the required air flow is determined as a functionof the fuelling rate. Although a throttle valve can and typically willbe used to control the air flow to the engine, the throttle valve doesnot regulate the engine speed as in conventional engines.

In either of these engine applications, idle speed control may occurboth when the motor vehicle is stationary and when the motor vehicle isin motion. However, if the control system performs closed loop idlecontrol when the motor vehicle is in motion, significant "driveabilityproblems" associated with the phenomenon commonly referred to as"tip-in/tip-out" can result. This phenomenon can manifest physically asrocking of the engine relative to the motor vehicle chassis duringacceleration, such as the throttle opening from idle (tip-in), ordeceleration, such as throttle closure to idle (tip-out).

Tip-out problems occur due to the engine being driven through thegearbox during vehicle motion whilst there is no operator demand on theengine, for example, such as when the throttle is closed. In the case offuelling controlled engines, this tends to maintain the engine speedirrespective of any attempt to control it by fuelling reduction.Accordingly, the closed loop idle control system, sensing thismaintained engine speed, typically reduces the fuelling to the enginesignificantly or totally in an attempt to reduce the engine speed to thetarget idle speed value. This generally causes a severe vehicledeceleration through the motor vehicle drive-line, which may typicallybe compounded by induced engine rocking. This is a very undesirablecondition which makes the motor vehicle very difficult to drivesmoothly.

Tip-in problems in fuelling controlled engines occur partly due to thefuelling rate being significantly reduced (due to closed loop idle)during tip-out as described above. As mentioned, this inducessignificant motor vehicle deceleration and engine rocking in the forwarddirection (in a transverse engine configuration) due to motoring throughthe gearbox. With regard to tip-in, the main problem arises in that,when the operator demand is once again applied, for example, such as thethrottle being re-opened, the fuelling level has to be increased veryrapidly to get from a significantly low level to the desired level for adrive away or acceleration condition, or too much lag will be felt inthe engine response. This however causes a very rapid change in enginetorque. This typically results in a reaction force causing the engine torock rearwards (in a transverse engine configuration) with significantforce resulting in a shock through the engine mounts and hence the motorvehicle.

Tip-in problems are compounded further on a motor vehicle having anautomatic transmission due to the desired low engine idle speed whenthere is no operator demand, such as when the motor vehicle isstationary, in order to reduce the torque converter load and to avoidwasting fuel. When a tip-in occurs from such a low idle speed and thechange in the fuelling rate is very rapid, the engine speed begins toincrease. However, from such a low idle speed, the engine speed has toincrease significantly before torque is transferred through the torqueconverter (or the "stall speed" thereof is reached) thus causing a timedelay in response to operator or driver demand for acceleration. As theengine speed increases, the rotating components thereof gather momentumand when decelerated by the torque converter, the energy acquired due tothis increasing momentum is dissipated as a severe shock through themotor vehicle drive-line. This is very undesirable and makes the motorvehicle difficult to drive smoothly.

The motor vehicle drive-line will typically include those componentsthat transmit the rotating energy of the engine to the driving wheels ofthe vehicle. In a vehicle with a transverse engine configuration, thedrive-line will include the engine gearbox or transmission whilst inconventional vehicles with rear wheel drive, the drive-line will alsoinclude for example the drive-shaft and the differential.

It is to be noted that these problems are potentially more pronounced inthe Applicant's engine which typically runs in a highly stratified mode(ie: has excess air). The fuelling rate of the engine may be increasedvery rapidly (ie: can be increased as such in one cycle) in response torapid changes in engine load demand and hence engine torque can risevery rapidly. Accordingly, there is a need for an alternative means ofcontrolling the engine idle speed during vehicle motion so as to improvethe tip-in and tip-out feel of the motor vehicle.

It is therefore an object of the present invention to provide improvedcontrol of the idle speed of an internal combustion engine which atleast substantially avoids one or more of the above noted problems.

SUMMARY OF THE INVENTION

With this in mind, the present invention provides in one aspect a methodof controlling the speed of an internal combustion engine of a motorvehicle comprising providing open loop control of the fuelling rate ofthe engine wherein the fuelling rate to the engine is modified when theengine is free of any operator derived load demand and when the engineis drive coupled to the vehicle wheels.

According to another aspect of the present invention, there is provideda control system for controlling the speed of an internal combustionengine of a motor vehicle wherein the control system provides open loopcontrol of the fuelling rate to the engine when the engine is free ofany operator derived load demand and when the engine is drive coupled tothe vehicle wheels.

Conveniently, a neutral response means may be provided to determine whenthe engine is not drive coupled to the vehicle wheels indicating thatopen loop control is not required. Such a neutral response means wouldindicate when the vehicle transmission is out of gear and could beimplemented on a manual or automatic transmission.

Conveniently, where the vehicle is fitted with a driver operated ormanual transmission between the engine and the wheels, a response means,such as a clutch switch, may be used to indicate when the engine isdrive coupled to the vehicle wheels. It is however to be noted thatother response means for establishing or indicating whether the engineis drive coupled to the vehicle wheels may be used such as a switchactuated when the drive train is in neutral.

Preferably the engine fuelling rate is controlled as a function of theengine speed and/or vehicle speed when the vehicle is moving above apredetermined vehicle speed.

Preferably, under open loop control, the engine fuelling rate iscontrolled as a function of the engine or vehicle speed with either ofthese being allowed to vary in response to engine operating conditions.This is different from closed loop control where the engine fuellingrate is controlled to maintain or return the engine speed to a targetvalue.

The engine is said to be drive coupled to the vehicle wheels when therotating components of the engine are doing work or are coupled to dowork to drive or turn the driving wheels of the vehicle. For example, ina vehicle having a manual transmission, the engine would be said to bedrive coupled to the vehicle wheels, or connected to the vehicledrive-line, when a gear is engaged and the engine clutch is engaged.Hence, if the vehicle operator depresses the clutch pedal to disengagethe clutch, the engine would not be drive coupled to the vehicle wheels.Equally, if the operator selects a neutral gear, the engine would not bedrive coupled to the vehicle wheels.

In a vehicle having an automatic transmission, the engine would be saidto be drive coupled to the vehicle wheels when a forward or reverse gearis selected and when torque is being transferred to the torqueconverter. Importantly, the engine would not be drive coupled to thevehicle wheels if the engine speed was below the stall speed of thetorque converter. Such a situation would equate to the engine idlingwhilst "in-gear" and no torque being transferred through the torqueconverter to drive or turn the driving wheels of the vehicle. Obviously,neutral being selected would also correspond to the engine not beingdrive coupled to the vehicle wheels.

It has been found that if the engine speed is controlled by way of anopen loop control system which controls the engine fuelling rate, theengine speed can settle to a particular value whereby there is a balancebetween the engine braking torque and the motoring torque appliedthrough the transmission, such as the gearbox, and drive-line of themotor vehicle. This results in a significant reduction or elimination ofundesirable tip-in and tip-out effects.

Preferably, open loop control of the fuelling rate of the engine isarranged to control the idle speed of the engine, particularly when thevehicle is moving.

Preferably, the open loop engine fuelling rate may be profiled such thata particular fuelling rate is provided for a particular engine speedand/or vehicle road speed independent of other factors. It is to benoted that, particularly in relation to four stroke cycle engineapplications, the fuelling rate at idle is dependent upon air flow intothe engine. Typically, the air flow is controlled by an idle speedcontrol valve. Accordingly, in such an application to achieve a fuellingprofile the control valve position could be profiled against enginespeed.

The profiling of the open loop control fuelling rate against engineand/or road speed may be such that the engine fuelling rate decreaseswith increasing speed and increases with decreasing speed. The loweringof the fuelling rate as the engine and/or road speed increases resultsin a reduction in the engine output torque. Thereby, when the vehicleoperator closes the throttle or removes the load demand from the engineat high engine/vehicle speeds, the motor vehicle induced motoring torquetransferred through the vehicle drive-line to the engine is greater thanthe engine output torque. This results in a braking/vehicle decelerationeffect. As the vehicle/engine speed decreases and the engine fuellingrate increases, the engine output torque continues to increase until itis in balance with the vehicle induced motoring torque, whereafter thevehicle/engine ceases to decelerate. This avoids "hanging up" of thevehicle/engine speed, (ie: the vehicle/engine speed being maintained ata level higher than is desired) and prevents severe deceleration whichwould result in the tip-out effects, as previously discussed, and henceimproves motor vehicle drivability.

To provide more accurate control of the engine fuelling rate as afunction of the engine speed, the control system may include at leastone open loop fuelling map, for controlling the fuelling rate as afunction of the engine speed when the control system is operating underopen loop idle. The open loop map may be obtained by experimental teststo determine the optimum fuelling rates for different road speeds of amotor vehicle which minimise tip-in/tip-out effects.

It may be convenient to also regulate the fuelling rate during open loopidle as a function of the particular gear ratio that has been selectedfrom the range available in the gearbox of the vehicle. To this end,separate open loop fuelling maps may be provided for selection dependenton the selected gear ratio of the vehicle transmission. Open loopfuelling maps may be provided for some or all of the selectable gearratios available. This would further enhance the open loop idle controlas the degree of motoring torque or load transferred from the gearbox tothe engine is significantly changed by the gear ratio selected.Therefore the fuelling rate and engine speed will settle to differentvalues in dependence on the selected gear ratio and the control achievedwould be less compromised than if a single open loop fuelling map wereused for all of the various gear ratios available in the vehiclegearbox.

The control system may also be sophisticated enough to apply fuellingoffsets to the or each open loop fuelling map to take account of anyparasitic loads which may be applied to the engine, such as from anair-conditioning compressor. In this way, the delivered fuelling ratesas a function of engine speed will ensure that the same engine outputtorque, as would be expected when no such parasitic load was applied tothe engine, would be maintained. Accordingly, the same vehicle/enginespeed deceleration rates can be maintained.

The control system may further include filter means to filter thefuelling rates of the open loop fuelling maps once open loop control hasbeen established and in the event that fuelling rates differsignificantly from the fuelling rates being delivered just before thecontrol system enters open loop control. In this way, rapid increases ordecreases in the mapped fuelling rates, due to the application of theopen loop fuelling map or maps, as profiled against engine speed can beprevented. Such rapid increases or decreases in the fuelling rate areundesirable as they may cause "shunt" in the vehicle drive-line.

The control system may also provide closed loop control of the enginespeed when there is no operator demand and the engine is disconnectedfrom the vehicle drive-line, wherein a target idle speed ispredetermined, and wherein the control system varies the fuelling rateto the engine to maintain the actual engine idle speed at leastsubstantially at the target idle speed. Preferably, the control systemprovides closed loop control of the engine speed when the motor vehicleis moving below the predetermined speed or is stationary.

The problems associated with tip-in/tip-out are at least substantiallyavoided by the present invention which typically allows the engine speedto settle to a level dependent on the balance of torques in the systemwhilst there is no driver or operator demand during vehicle motion (ie:idle at a higher engine speed than would otherwise be the case) andwhich also or alternatively, does not reduce the fuelling rate to theengine if the engine is being driven through the gearbox as is typicallythe case under normal closed loop control whilst the motor vehicle is inmotion and there is no driver demand.

The invention will be more clearly understood from the followingdescription made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing the operation of the control systemaccording to the present invention; and

FIG. 2 is a diagram showing the relationship between the fuelling rate(FPC) and the engine speed (RPM) or vehicle speed when the controlsystem is providing open loop control.

FIG. 3 is a diagram showing the relationship of the control unit toother elements of the control system.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1, the flowchart shows the operation of thecontrol system during periods of idle when there is no driver demand onthe engine. The control unit 1 periodically checks whether theaccelerator pedal 2 controlling the engine fuelling rate is disengagedwhich indicates when the engine is in an idling or no load mode ofoperation. If the accelerator or demand pedal is engaged or depressed,then the control system maintains its normal engine management controlfor the engine when under load. As previously alluded to hereinbeforeand particularly in the case of four stroke engines, the control systemmay alternatively periodically check whether the throttle controllingthe air to the engine is closed which would similarly indicate that theengine is in an idling or no load mode of operation. Further, it is tobe noted that the control system is not limited to controlling theengine idle speed and can be implemented to control the off-idle enginespeed as well.

If the accelerator pedal is disengaged by the driver or operator of thevehicle, the control system then checks an engine speed sensor 3 todetermine whether the engine speed is less than the idle entrythreshold. This engine speed can be determined by experimentation andmay be profiled against vehicle road speed as discussed brieflyhereinafter. In this regard, the idle entry threshold may be higher forlower vehicle road speeds and lower for higher vehicle road speeds. Ifthe engine speed is not less than the idle entry threshold, the controlsystem switches to over-run fuel cut-off mode wherein fuelling to theengine is ceased in the known manner.

If the engine speed is less than the idle entry threshold, the controlsystem then enters an idle mode of operation. In the embodiment asdescribed, the control system checks to see whether the engine isconnected to the vehicle drive-line. As alluded to hereinbefore,depending on the nature of the vehicle transmission, a clutch switch 4and/or a neutral switch may be used to determine this. Alternatively,such a determination may be made from the vehicle road speed.

If the engine is not connected to the drive-line, the control systemswitches to closed loop idle control. In a vehicle with a manualtransmission, this would equate to the situation where, for example, theclutch was disengaged and the engine 5 was not causing the gearbox 6 andhence the driving wheels to turn. In a vehicle having an automatictransmission, this would equate to the situation where the transmissionwas in neutral. Under this closed loop idle control, the actual idlespeed of the engine is periodically compared with a desired target valueand returned to that target value when any deviation occurs.

In the case where the vehicle's road speed is used to determine whetherto enter closed loop idle control, this method being particularlyapplicable to vehicles having an automatic transmission, the controlsystem may check whether the motor vehicle's road speed is greater thana predetermined road speed. This closed loop entry road speed cantypically be within the range from 1 km/hr to 10 km/hr, although it isto be appreciated that the predetermined speed will vary depending onthe engine performance characteristics and other parameters.Accordingly, the control system switches to closed loop idle control ifthe motor vehicle speed is less than this closed loop entry speed.

Such control of the engine idle speed is acceptable when the motorvehicle is at rest because the tip-in/tip-out effects as mentionedhereinbefore are not relevant at such instances. However, when the motorvehicle is in motion, tip-in/tip-out can become a problem and adifferent form of engine idle speed control is required to minimise orprevent such effects. Therefore, when the engine is connected to thedrive-line, the control system switches to open loop idle control. Thecontrol system remains in this mode of operation until the motor vehiclespeed drops below the closed loop entry speed or the accelerator isdepressed or engaged.

The previously mentioned clutch and/or neutral switches may again beused to provide the determination that the engine is connected to thedrive-line. In a vehicle having a manual transmission, this would equateto the clutch being engaged and the transmission being in-gear. In avehicle having an automatic transmission, this would equate to thetransmission being in-gear (ie: not in neutral) and the engine speedbeing greater than the stall speed of the torque converter such thattorque generated by the engine is being transferred to the gearbox andhence drive-line of the vehicle. In the case where vehicle road speed isused to determine whether to switch to open loop idle control, thiswould equate to the motor vehicle speed being above the closed loopentry road speed.

In the Applicant's engine, commonly known as the OCP engine, the enginefuelling rate normally directly controls the engine output torque andthe resultant engine speed. The engine fuelling rate is controlled as afunction of the engine speed or road speed during open loop control ofthe engine. The control system can use an "open loop fuelling map" basedon the characteristic as shown in FIG. 2 which provides a fuelling rateas a function of the engine speed or road speed. In the flowchart ofFIG. 1, engine speed has been used.

At lower engine speeds, the fuelling rate is higher providing higherengine torque. Therefore tip-in problems arising as the motor vehicle isaccelerated and hence the speed of the engine is caused to accelerateare minimised because the rate or level of increase of the engine torqueis reduced thereby reducing the shock through the drive-line of themotor vehicle. At higher engine speeds, the fuelling rate is arranged tobe lower than at the lower engine speeds. This results in an overalllower engine torque which increases engine braking and graduallydecelerates the motor vehicle and prevents any "hang-up" of the enginespeed.

The control system may also take into account any parasitic loads thatmay be applied to the engine when it switches to or is running open loopidle control. In this regard, offsets may be applied to the open loopfuelling map to ensure that a certain engine output torque is maintainedfor a particular engine speed when, for example, an air-conditioningcompressor is applying a load on the engine.

Further, the control system may apply a filter means to the calculatedopen loop fuelling levels to dampen out any rapid increases or decreasesin the fuelling levels to the engine. In this way, "shunt" in thevehicle drive-line can be prevented and hence good vehicle drivabilitycan be maintained.

The degree of motoring torque applied to the engine through the gearboxvaries significantly with changes in gear ratio. Separate open loopfuelling maps can therefore be provided, one for each or some of thegears of the engine gearbox. This further enhances the operation of thecontrol system during open loop control. It is of course possible to useonly a single open-loop fuelling map, the fuelling profile of the mapbeing a compromise between the various gears. Such gear dependent openloop fuelling maps would also enable a lower fuelling rate and henceidle engine speed to be selected for higher gears were tip-in andtip-out are not so severely affected by the lower engine speed andshocks through the motor vehicle drive-line are not so severe.

As alluded to hereinbefore, it is also possible to profile the thresholdengine speed for engine over-run fuel cut-off situations as road speedchanges. At low vehicle road speeds, higher threshold engine speeds arerequired as tip-in and tip-out effects are more significant. Such higherthreshold engine speeds will provide better drivability. At high vehicleroad speeds, vehicle inertia results in any tip-in or tip-out effectsbeing less significant and so lower threshold engine speeds for engineover-run fuel cut-off situations may be used. Accordingly, in thislatter regard significant fuel economy benefits may be obtained and gooddrivability maintained by lowering the threshold engine speeds asvehicle road speed increases.

Although the method is generally described in relation to the OCPengine, it is to be appreciated that the control strategy is alsoapplicable to other internal combustion engines including four strokeengines. Further, although the method is generally described in relationto the engine fuelling rate being controlled as a function of enginespeed, road speed may equally be used.

I claim:
 1. A control system for controlling the speed of an internalcombustion engine of a motor vehicle wherein the control system providesopen loop control of the fuelling rate to the engine when the engine isfree of any operator derived load demand and when the engine is drivecoupled to the vehicle wheels.
 2. A control system according to claim 1,wherein the control system includes at least one open loop fuelling mapfor controlling the fuelling rate as a function of the engine speed. 3.A control system according to claim 2, wherein the open loop fuellingmap decreases the engine fuelling rate with increasing engine speed andincreases the engine fuelling rate with decreasing engine speed.
 4. Acontrol system according to claim 2, wherein the motor vehicle includesa gearbox and the control system includes a plurality of open loopfuelling maps, the control system selecting a said map as a function ofa selected gear of the gearbox.
 5. A control system as claimed in claim2 wherein a fuelling offset or offsets are provided for at least one ofsaid maps to compensate for a parasitic load or loads on the engine. 6.A control system according to claim 1 wherein the open loop control ofthe fuelling rate is a function of speed.
 7. A control system accordingto claim 1 wherein the open loop control of the fuelling rate is afunction of road speed.
 8. A control system according to claim 1,wherein the control system further provides closed loop control of theengine fuelling rate whereby the fuelling rate is controlled to maintaina target engine speed when the motor vehicle is moving below apredetermined speed.
 9. A control system as claimed in claim 1 whereinthe control of the fuelling rate is only effected when the vehicle istravelling at a speed above a predetermined speed.
 10. A control systemas claimed in claim 1 wherein means responsive to the absence of a driveconnection between the engine and the vehicle wheels is provided toinhibit establishment of the open loop control of the fuelling rate whenno drive connection exists.
 11. A control system as claimed in claim 10wherein said responsive means respond to de-coupling of a gear trainbetween the engine and the vehicle wheels.
 12. A method of controllingthe speed of an internal combustion engine of a motor vehicleincluding:a) determining whether the engine is free of any operatordemand; b) determining whether the engine is connected to the vehicledrive line; c) providing open loop control of the fuelling rate of theengine when the engine is free of any operator load demand and theengine is connected to the vehicle drive line; d) providing closed loopcontrol of the fuelling rate of the engine when the engine is free ofany operator demand and the vehicle engine is not connected to thevehicle drive line; and e) providing normal control of the enginefuelling rate when there is an operator demand on the engine.
 13. Amethod according to claim 12, wherein the engine is free of operatordemand when an accelerator pedal of the vehicle is disengaged.
 14. Amethod according to claim 12, wherein the engine is free of operatordemand when an inlet air throttle valve of the vehicle is closed.
 15. Amethod of controlling the speed of an internal combustion engine of amotor vehicle comprising providing open loop control of the fueling rateof the engine wherein the fuelling rate to the engine is modified whenthe engine is free of any operator derived load demand and when theengine is drive coupled to the vehicle wheels.
 16. A method as claimedin claim 15 wherein the fueling rate is controlled to promotemaintenance of a selected engine speed.
 17. A method as claimed in claim15 wherein said control of the fueling rate is only effected when thevehicle is travelling at a speed above a predetermined vehicle speed.18. A method as claimed in claim 15 wherein the open loop control of thefueling rate is controlled as a function of engine speed.
 19. A methodas claimed in claim 15 wherein the open loop control of the fueling rateis controlled as a function of vehicle road speed.
 20. A method asclaimed in claim 15 wherein the fueling rate is controlled to establishand/or control the engine speed to a target speed when the vehicle istravelling below a preselected speed.
 21. A method as claimed in claim15 wherein the open loop control of the fueling rate of the engine isarranged to control the idle speed of the engine.
 22. A method asclaimed in claim 15 claims wherein the fuelling rate to the engine ismodified by the application of a fueling offset to account for aparasitic load on the engine.
 23. A method according to claim 15,including decreasing the engine fuelling rate with increasing enginespeed and increasing the engine fuelling rate with decreasing enginespeed under open loop control of the engine.
 24. A method according toclaim 15, including further controlling the engine fueling rate as afunction of a selected gear of the engine under open loop control.